1. Field of the Invention
The present invention relates to a rod-shaped workpiece grinder for use in grinding a front end surface of a very small rod-shaped workpiece into a spherical or flat surface.
2. Description of the Prior Art
In the case of a very small rod-shaped workpiece such as a ferrule (diameter: 2.5 mm, length: 12.7 mm, material: zirconia ceramics) to be used for an optical fiber connector, there is performed transmission of light by making front end surfaces of ferrules abut on each other with an optical fiber having a diameter of, for example, 0.05 mm inserted in a center hole of each of the ferrules. Therefore, the front end surfaces of the ferrules are each processed in a spherical form so that the centers of the optical fibers are correctly aligned with each other and no leak of light is assured.
Conventionally, in grinding the front end surface of such very small rod-shaped workpiece into a spherical surface, a grinder as shown in FIG. 16 has been used.
The grinder is comprised of a diaphragm chuck 1 and a grinding wheel 2. The diaphragm chuck 1 has a structure for supporting and rotating a rod-shaped workpiece W. On the other hand, the grinding wheel 2 has a cup shape and is formed with a grinding surface 2a which inclines inward from its peripheral edge portion. The axial center of the grinding wheel 2 is tilted by a specified angle with respect to the axial center of the rod-shaped workpiece W.
Grinding of the rod-shaped workpiece W by this grinder is performed by holding one end of the workpiece W by the diaphragm chuck 1 to rotate the workpiece W, and putting the rotatively driven grinding wheel 2 in abrasive contact with the other end of the workpiece W.
However, the above-mentioned conventional grinder has the following problems.
Firstly, a desired processing accuracy is hardly obtained. That is, since the diaphragm chuck 1 is used for supporting the rod-shaped workpiece W, a misalignment between the center of rotation of the chuck and the axial center of the rod-shaped workpiece W cannot be eliminated (misalignment amount: 50 .mu.m). Particularly in the case of a ferrule, high-accuracy finish dimensions are required as described above (dimensional accuracy: .+-.10 .mu.m, R dimension: .+-.0.5 mm, shape: 0.15 .mu.m, surface roughness: 0.01 .mu.mRa, concentricity: 20 .mu.mTIR), and therefore the influence of the misalignment on the processing accuracy cannot be ignored. Furthermore, since the grinding wheel 2 is put in surface contact with the rod-shaped workpiece W, the finishing accuracy is influenced by the surface roughness and shape of the grinding surface 2a. In addition, a coolant is not smoothly supplied to the grinding surface 2a, and therefore the desired grinding condition cannot be obtained. Furthermore, in the case of spherically grinding the rod-shaped workpiece W, in addition to the shape of the grinding surface 2a, the degree of tilt of a rotary drive shaft of the grinding wheel 2 with respect to the axial center of the rod-shaped workpiece W emerges as a problem, however, angle adjustment for achieving the tilt is difficult.
Secondly, the grinding wheel 2 has a short operating life. That is, as described above, the grinding wheel 2 processes the rod-shaped workpiece W for grinding in surface contact with the rod-shaped workpiece W, and therefore the grinding wheel 2 will be worn away soon. Furthermore, the grinding wheel 2 is set tilt, and therefore the grinding wheel 2 is put in contact with the other portion of the grinder, for example, a mounting portion of the diaphragm chuck 1. Therefore, the outer diameter dimension of the grinding wheel 2 is not allowed to have a value not smaller than a specified value. Therefore, a cycle of replacing the grinding wheel 2 is short.
Thirdly, there are required at least two moving axes to be subjected to an NC control. That is, there are required at least an axis for feeding the grinding wheel 2 for grinding and an axis for tilting the grinding wheel 2, and control therefor is complicated.
Fourthly, there is bad workability. That is, in the stage of mounting and dismounting of the rod-shaped workpiece W to and from the diaphragm chuck 1, an axial movement of the rod-shaped workpiece W, i.e., inserting and pulling of the rod-shaped workpiece W into and out of the diaphragm chuck 1 is required, and therefore a cycle time of 40 to 50 seconds has been required. Furthermore, the tilt angle setting of the axis of rotation of the grinding wheel 2 has been difficult, and this has required much time.